Semi-Blind Nanoprobing for Enhanced Device Testing

One of the key challenges in nanoprobing is the degradation of the device under test (DUT) due to continuous exposure to the electron beam. This application example demonstrates how the SmarProbe effectively eliminates beam-induced degradation—even at higher beam energies—enabling reliable nanoprobing of sensitive samples across all types of SEM systems.

Beam-induced degradation can significantly alter device characteristics. For example, during transistor probing, the electron beam may cause surface charging, which leads to shifts in threshold voltage and changes in channel conductivity. The extent of degradation is primarily influenced by two key parameters:

• Beam energy
• Exposure duration

Figure 1 illustrates this effect by showing the threshold voltage shift of a pFET transistor fabricated using FD-SOI technology. The dataset was acquired using the high-precision SmarProbe nanoprober from SmarAct, ensuring nanometer-scale stability and constant contact resistance throughout the measurement process of more than 35 minutes.

Fig. 1: Transistor degradation during SEM imaging. The SmarProbe allows probing of a complete 6T memory cell in less than 2 seconds of accumulated imaging time.

Degradation effects are observable after just one minute of exposure at both 100 eV and 200 eV beam energies, with the impact being significantly more pronounced at 200 eV. Although degradation proceeds more slowly at 100 eV, this energy level also results in substantially reduced image quality, which significantly slows down the probing process. Consequently, nanoprobing based on visual feedback—where probe placement is manually guided via SEM imaging—is impractical for beam-sensitive samples.

To circumvent this limitation, such samples are typically analyzed using an Atomic Force Prober (AFP), which enables contact without the need for electron beam-based imaging. As an innovative alternative, the SmarProbe nanoprober enables semi-blind nanoprobing. This method allows the reliable probing of a complete 6T memory cell in less than 2 seconds of total SEM imgaing time —a duration during which no measurable degradation compared to the values from AFP measurements was observed. This approach combines high precision with minimal beam interaction, offering a powerful solution for sensitive device characterization and an alternative to AFP.

Fig.2: Uncut video of the semi-blind nanoprobing. PU, PD and PG transistors were probed in series at 200 eV without any beam-induced degradation.

The semi-blind nanoprobing capability of the SmarProbe system is made possible by three core features that ensure precise, reliable, and repeatable probe placement with minimal electron beam exposure:

1. Fully encoded probes and sample positioning, with closed-loop control at 1 nm resolution
2. Active temperature stabilization to suppress thermal drift under all environmental conditions
3. Automated probe landing on a all surface types

Together, these features allow SEM imaging to be limited to discrete steps—only after each probe or sample movement is completed. For instance, an initial SEM image (acquired with a cycle time of 120 ms at 200 eV) provides positional feedback. From this image, a user can perform point-and-click targeting to guide a probe precisely onto a transistor contact pad. Once the target position is reached, a follow-up image is captured to verify probe placement. Thanks to the system’s active position-holding capability, the probe remains stable, with no drift or piezo creep.

This process is repeated for the remaining probes, typically requiring only 6 to 9 images to complete the setup for all contact pads. Once positioned, the SmarProbe can automatically characterize multiple transistors in succession, provided the relative pad locations are known—such as from CAD layout data. As a result, three transistors can be probed in a row with a total SEM exposure time of just 1.3 seconds, effectively eliminating beam-induced degradation. This highly efficient probing workflow is demonstrated in the accompanying video.